In the combustion of a fuel (e.g., coal, oil, peat, waste, biofuel, natural gas, or the like used for the generation of power or for the production of materials such as cement, steel or glass, or the like, a stream of hot flue gas (also sometimes known as process gas) is generated. Such a hot flue gas contains, among other components, carbon dioxide (CO2).
A chilled ammonia process (CAP) is often used for the removal of carbon dioxide (CO2) from a post-combustion flue gas stream. The chilled ammonia process provides a relatively low cost means for capturing and removing carbon dioxide from a gas stream, such as, for example, a post combustion flue gas stream.
In the chilled ammonia process, the absorption of carbon dioxide from a flue gas stream is achieved by contacting a chilled ammonia ionic solution with a flue gas stream containing carbon dioxide. This is generally accomplished in a capture system (also termed an “absorber system”). The ionic solution containing absorbed carbon dioxide is subsequently regenerated, whereby carbon dioxide is removed from the ionic solution, and the regenerated ionic solution is reused in the carbon dioxide absorption process. This is generally accomplished in a regeneration system. Thus, a circulating stream of ionic solution is formed, which circulates between the capture system and the regeneration system. The ionic solution may be composed of, for example, water, ammonia, ammonium sulfate, carbon dioxide and derivatives thereof.
Moisture in the flue gas can accumulate in the ionic solution as it circulates between the capture system and the regeneration system. In order to remove this moisture from the ionic solution, an appendix stripper configured as a gas-liquid contacting device, receives a portion of the circulating ionic solution. In this device, warm ionic solution is depressurized to form a gas phase containing the vapor of low boiling point components of the solution (primarily ammonia and carbon dioxide), and a liquid phase containing the high boiling point components of the solution. A portion of the gas phase compound is absorbed in the residual flue gas stripping medium and returned to the chilled ammonia process absorber vessels. The liquid phase containing the ammonium sulfate is sent to the direct contact cooler system for purge with the ammonium sulfate bleed stream.
The use of steam in the appendix stripper however involves operating temperatures which promotes dissociation of the ammonia sulfate into acidic compounds, which tends to corrode other equipment used in the gas-liquid separating device.